1. Field of the Invention
This invention relates to improvements in devices and methods for making and/or replicating color transparencies, such as color slides and cine film. Moreover, it relates to a unique silverless recording element for color imaging.
2. The Prior Art
The use of an additive color filter screen to produce, in cooperating with a pan-sensitive, black-and-white silver halide emulsion, a positive color transparency is well known. According to the once commercial Dufaycolor process, the silver halide emulsion is imagewise exposed through the color screen to produce a black-and-white image containing color information of the subject. The color screen, which may be separable or inseparable from the silver halide layer, typically comprises a mosaic of red, green and blue filter elements which may be random or regular in their arrangement. Upon developing the silver halide layer by the reversal process, illuminating the resulting image with white light and viewing the image through the color screen, the colors of the original subject are seen. The synthesis of the colors of the original subject is obtained by the additive mixture of the light transmitted by the many small red, green and blue filter elements of the screen. The Dufaycolor process is disclosed in U.S. Pat. No. 1,003,720 issued to Dufay, and discussed in Photography--Its Materials and Processes, by Neblette, 6th Edition (1962), pp. 431-435. Reference can also be made to History of Color Photography by Friedman, 1944, Chapters 12-14.
In addition to the above-mentioned Dufaycolor color imaging process, the currently commercial Polavision process represents another example of a process which makes use of the combination of an additive color screen and a silver halide emulsion to produce full color transparencies. This process, which makes use of silver diffusion transfer technology, is disclosed, for example, in U.S. Pat. No. 3,990,895 issued to Land.
In the color imaging processes of Dufay and Land, the developed silver halide emulsion functions merely as a mask to block out, or at least reduce the intensity of, those color components of the illuminating white light source which were either not present or subdued in the original subject. Silver-containing emulsions, of course, tend to be costly in terms of raw materials and manufacturing costs; moreover, most silver emulsions require liquid processing. Thus, it would be desirable to find a silverless substitute.
Two interesting classes of silverless, yet radiation-sensitive, materials which might be considered as substitutes for the silver-containing emulsions mentioned above are the vesicular and diazotype materials. Such materials are relatively inexpensive to make and simple to process; further, these materials can be made virtually transparent to visible radiation. Unfortunately, however, vesicular and diazotype materials have heretofore been disqualified for use in the above process as a result of their insensitivity to visible radiation. Vesicular materials, for example, are primarily sensitive to near ultraviolet radiation, the maximum wavelength of sensitivity being about 3850 A. Only a few specially sensitized diazotype materials exhibit a maximum wavelength sensitivity of 5000 A. Hence, neither of these materials is capable of "seeing" subjects of all colors in the visible spectrum (i.e. from 4000 to 6500 A).
In Research Disclosure No. 14219, February 1976, there is disclosed the concept of using a toner image, formed on a photoconductive layer by the well-known electrographic process, as a mask through which a vesicular layer can be imagewise exposed. The photoconductive and vesicular layers form two layers of multilayer recording elements. In use, the photoconductive layer is imagewise exposed to visible radiation to form a latent electrostatic image. This latent image is then developed with a black pigment (i.e. toner) and the vesicular layer is then flash exposed to ultraviolet radiation through the toner image on the photoconductive layer. Such a laminar construction of the recording element and the two exposure steps enable visible radiation from the original subject to be recorded in the vesicular layer. This process, however, is inherently a monochrome process and offers no capability of recording full color images.